1. Field of the Invention
The present invention relates to a spring having improved durability as compared to a conventional spring.
2. Description of the Related Art
In recent years, motorcycles used for specific applications such as racing or the like utilize springs made of Ti. Springs made of Ti are lightweight as compared to conventional springs made of Fe. For example, a suspension unit that has a Ti spring may weigh 200 to 500 g (by spring constant) less than a suspension unit that utilizes a conventional spring made of Fe.
When replacing a spring made of a high strength material with a spring made of a lower strength material, the spring wire diameter must be increased in order to maintain the same spring strength. For example, when a spring made of Fe is replaced with a spring made of Ti that has the same spring constant, the wire diameter of the Ti spring must be increased to maintain the same strength as the Fe spring.
Consequently, the larger Ti spring, which is retrofitted onto a suspension unit designed for a Fe spring, has reduced clearance between the Ti spring and a cylinder of the shock absorber. This decrease in clearance may increase the chance that a compressed Ti spring contacts the cylinder and may reduce the durability of the Ti spring.
U.S. Patent Application No. 2002/0105127 proposes a spring that bends relative to a central axis thereof. The spring has first turns on both ends of the spring that are inclined relative to the spring bearing members at a predetermined angle. However, having the spring bend relative to the central axis may increase the chance that the spring may buckle when the spring is compressed. This bucking may then lead to the spring contacting the shock absorber cylinder of the suspension unit.